The present invention relates to a multistage rotating speed control circuit for a DC motor.
Concerning the rotating speed control of a DC motor, there are two kinds of control circuits: (1) the first kind of control circuit can provide only fixed rotating speed of a DC motor; (2) the second kind of control circuit can provide multistage rotating speed of a DC motor. Since the rotating speed of a DC motor cannot be adjusted using the former control circuit, an additional speed change device is necessary to enable multistage rotating speed of a DC motor, which is not convenient. On the other hand, the latter utilizes the 8255A interface circuit used in the 8-bit microprocessor 8085A and Z80 to achieve the function of multistage rotating speed control of a DC motor, which requires complicated circuitry and high cost.
FIG. 1 is a block diagram showing the digital rotating speed control circuit for a DC motor of the U.S. patent application. Ser. No. 08/988,051, wherein a digital circuit is used to control the rotating speed of a DC motor. The digital circuit receives an input digital signal set (CONl.about.CONn) which can be generated by, for example, a microcomputer accompanied with an A/D interface card. However, it requires high cost because the system is complicated.
In view of the above, the purpose of the present invention is to provide a circuit composed of simple electric elements, by which an input digital signal set (CONl.about.CONn) for a digital control circuit can be generated.